Image scanners are widely used for scanning images of documents, photographs or films. The scanned images can be converted into electronic files, which are then stored, processed or spread. With increasing development of scanning technologies, the image scanners have experienced great growth and are now rapidly gaining in popularity.
In the early stage, the image scanner can scan one side of the document. For scanning both sides of the document, after one side of the document has been scanned, the document should be manually turned over so as to scan the other side of the document. However, the process of manually turning over the document is troublesome. Recently, a duplex scanning apparatus has been developed for automatically performing a duplex scanning operation to scan both sides of the document.
A typical duplex scanning apparatus usually comprises a flatbed image scanning portion and an automatic document feeder arranged above the flatbed image scanning portion. The flatbed image scanner portion is utilized to scan most documents regardless of a single sheet or a thick book. In a case that the thick book is scanned, the automatic document feeder is not feasible. For performing the duplex scanning operation, a stack of paper sheets are successively and continuously fed by the automatic document feeder to be transported through a scan region in the flatbed image scanning portion. For most duplex scanning apparatuses, the flatbed image scanning portion has one scanning module responsible for scanning both sides of the document. After scanned, the paper sheets are exited to the sheet ejecting tray.
Generally, for performing the duplex scanning operation by the duplex scanning apparatus having one scanning module while rearranging the scanned documents in the same order as the original stack, the documents need to be transported across the scan region for three times. Therefore, such a duplex scanning operation is referred as a three-pass scanning operation. When the document is transported across the scan region for the first time, the scanning module scans a first side of the document. When the document is transported across the scan region for the second time, the scanning module scans a second side of the document. Finally, the document is transported across the scan region for the third time to rearrange each document into the same order as the original stack but the scanning module does not scan the document. The three-pass scanning operation of the duplex scanning apparatus, however, is relatively time-consuming. For increasing the scanning speed, a duplex scanning apparatus for performing a two-pass scanning operation has been developed. In the two-pass scanning operation, the documents need to be transported across the scan region for two times.
For example, U.S. Pat. No. 6,648,320 (also referred hereinafter as '320 patent) discloses a duplex scanning apparatus for performing a two-pass scanning operation while rearranging the scanned documents in the same order as the original stack. FIG. 1 is a schematic cross-sectional view illustrating a duplex scanning apparatus according to a first embodiment of the '320 patent. The duplex scanning apparatus 100 of the '320 patent includes a flatbed image scanning portion 101 and an automatic document feeder 113. The flatbed image scanning portion 101 includes a light source 116, several reflective mirrors 117, a lens 118 and an image receiving element 119. The automatic document feeder 113 includes a sheet input tray 102, a first sheet ejecting tray 1031, a second sheet ejecting tray 1032, a sheet pick-up roller 112, a first transfer channel 104, a second transfer channel 106, a third transfer channel 105, a first ejecting channel 108, a second ejecting channel 109, a first inverting channel 110, a second inverting channel 107, a first switching element 121, a second switching element 122, a third switching element 123, a fourth switching element 124, a scan region 115, a first inverting region 120, a second inverting region 111, a first inverting roller assembly 125 and a second inverting roller assembly 114.
Please refer to FIG. 1 again. Hereinafter, a procedure of performing a single-side scanning operation by the duplex scanning apparatus 100 according to the '320 patent is illustrated. First of all, multiple documents (not shown) to be scanned are placed on the sheet input tray 102. Then, the sheet pick-up roller 112 transports a first document into the first transfer channel 104. Then, the roller assembly beside the first transfer channel 104 transports the document into the second transfer channel 106. When the document is transported across the scan region 115, the light beams emitted from the light source 116 of the flatbed image scanning portion 110 are projected on the documents and reflected by the reflective mirrors 117. The reflected light beams are focused by the lens 118 onto the image receiving element 119. After receiving the focused light beams, the image receiving element 119 outputs corresponding image signals to a computer which is linked to the duplex scanning apparatus 100. After the document has been scanned, the first switching element 121 is switched to open the third transfer channel 105 such that the document is transported to the first sheet ejecting tray 1031 through the third transfer channel 105 and the second ejecting channel 109. Alternatively, after the document has been scanned, the first switching element 121 is switched to open the first ejecting channel 108 such that the document is transported to the second sheet ejecting tray 1032 through the first ejecting channel 108.
Hereinafter, a procedure of performing a duplex scanning operation by the duplex scanning apparatus 100 according to the '320 patent is illustrated. First of all, multiple documents (not shown) to be scanned are placed on the sheet input tray 102. Then, the sheet pick-up roller 112 transports the first document into the first transfer channel 104. Then, the document is transported to the scan region 115 through the second transfer channel 106. When the document is transported across the scan region 115, a first side of the document is scanned. After the first side of the document has been scanned, the first switching element 121 and the second switching element 122 are switched to a position leading the document to the first ejecting channel 108. Next, the document is nipped between the rollers of first inverting roller assembly 125 and transported to the first inverting region 120. Until the tail edge of the document is transported across the second switching element 122 and then nipped between the rollers of the first inverting roller assembly 125, the second switching element 122 is switched to open the first inverting channel 110. Meanwhile, the first inverting roller assembly 125 is rotated in a reverse direction to transport the document into the first inverting channel 110. Next, the document is transported to the scan region 115 through the second transfer channel 106 again. When the document is transported across the scan region 115, a second side of the document is scanned. After the second side of the document has been scanned, the first switching element 121 is switched to open the third ejecting channel 105 such that the document is transported to the third ejecting channel 105. Next, the fourth switching element 124 is switched to lead the document to the second inverting region 111. After the tail edge of the document passes through the fourth switching element 124, the fourth switching element 124 is switched to open the second inverting channel 107. Then, the second inverting roller assembly 114 is rotated in a reverse direction to transport the document into the first sheet ejecting tray 1031. Meanwhile, the duplex scanning operation is completed.
As previously described, during a duplex scanning operation of the duplex scanning apparatus 100, the document needs to be transported across the scan region for two times. After the second side of the document has been scanned, the document is led to the second inverting region 111 to be rearranged in the same order as the original stack, instead of being sent to the first sheet ejecting tray 1031 or the second sheet ejecting tray 1032. In comparison with the duplex scanning apparatus performing the three-pass scanning operation, the duplex scanning apparatus 100 of the '320 patent has a higher scanning speed.
The duplex scanning apparatus 100 of the '320 patent, however, still has some drawbacks. For example, due to spatial hindrance, the first sheet ejecting tray 1031 can accommodate relatively small-sized documents. Whereas, the document having a size greater than a special size needs to be ejected to the second sheet ejecting tray 1032. In other words, the document having a size greater than the special size needs to be transported across the scan region 115 for three times in order to rearrange the document in the same order as the original stack. Under this circumstance, the speed of scanning the large-sized document by using the duplex scanning apparatus 100 of the '320 patent is not high enough. Therefore, the '320 patent further disclosed another duplex scanning apparatus for increasing the speed of scanning the large-sized document.
FIG. 2 is a schematic partially cross-sectional view illustrating a duplex scanning apparatus according to a second embodiment of the '320 patent. In the second embodiment of the '320 patent, only one sheet ejecting tray is included and the sheet ejecting roller assembly is modified. Hereinafter, a procedure of performing a duplex scanning operation by the duplex scanning apparatus 200 according to the '320 patent is illustrated with reference to FIG. 2. First of all, a document to be scanned is transported to the scan region 215 through the first transfer channel (not shown) and the second transfer channel 206. When the document is transported across the scan region 215, a first side of the document is scanned. After the first side of the document has been scanned, the first switching element 221 and the second switching element 222 are switched to lead the document to the ejecting channel 208. Next, the document is transported to the first inverting region and nipped between the driving roller 2141 and the follower roller 2142 of the inverting roller assembly 214. Until the tail edge of the document is completely detached from the ejecting channel 208, the second switching element 222 is switched to open the first inverting channel 210. Next, the document is transported to the scan region 215 through the first inverting channel 210 and the second transfer channel 206. When the document is transported across the scan region 215, a second side of the document is scanned. After the second side of the document has been scanned, the first switching element 221 and the third switching element 223 are switched to open the third transfer channel 205 such that the document is transported to the second inverting region 211. Next, the third switching element 223 are switched to open the second inverting channel 207 such that the document is transported to the sheet ejecting tray 203 through the second inverting channel 207. Meanwhile, the duplex scanning operation is completed. Since the sheet ejecting tray 203 can accommodate large-sized documents, the document of diverse sizes can be scanned by the duplex scanning apparatus 200 while the scanned document is transported across the scan region 215 for only two times.
Although the document is transported across the scan region for only two times by the duplex scanning apparatus of the '320 patent, the document is still inverted for two times in order to perform each duplex scanning operation. In other words, since the inversion path is shortened, the duplex scanning operation performed by the duplex scanning apparatus of the '320 patent has increased scanning speed in comparison with the three-pass scanning operation. For further increasing the scanning speed of performing the duplex scanning operation, there is a need of providing for performing a two-pass scanning operation while inverting the document for only one time.